: : The previous discussion at the link doesn't really answer the poster's question. Maybe no one knows why "There, there" is used in comforting. If I had to guess, I'd say the th- sound might be calming. It sounds soft, like a cushion. (Do speakers of languages with harsher consonants say the equivalent of "There, there"?) And the meaning of the word may ground comfortees by emphasizing their location in their bodies. ~rb

: Exact reduplications like 'there, there' are often used in baby talk - 'choo-choo', wee-wee' etc. I'm not sure why.

Good point, Gary, and one that implies that when we are at a very low point, even if babyhood is long past, baby talk can be soothing. "There, there" is often heard from someone trying to succor a soul in distress. As for the use of reduplicative baby-talk with real babies, there is a vigorous debate going on as to whether it is, in fact, helpful in the process of getting the baby to understand and start to talk, or a hindrance.

The OED has not overlooked "there, there":
[After citing other uses of "there" interjectionally,] "Hence there-there vb. trans., to soothe or comfort by saying these words."